I've seen some people switching from carbs to fast efi and similar efi systems on their 351m and 400 motors.. people that have done this, what's your mpg before and after, horsepower feel?

 

I dought if you feel a HP feel. The engine will just start Cold and run better from then on. Mpg,s are a bonus if there are any. Don,t count on that. Driveability is supposed to be much better.A fine tuned carb does a good job too.

 

I'd kinda like the know the answer to this too. I'm not expecting a huge increase but I bet at least 75% of the vehicles I see with carbs aren't running the way they should. Most people don't know how to tune a carb properly. I'll admit I have to play with them a while and always wonder if there's more in it after I'm satisfied.

 

Comparing to a very well tuned carb the main EFI benefit would be starting, fuel flexibility (varying alcohol no problem for EFI), altitude flexibility and longer engine life.

Longer life comes from less fuel wash down of the cylinder walls. On my carb dent, for example, shutdown after running in hot weather boils the gas out of the carb. On re-start, it is collected in the intake and runs pig rich for a few seconds. Not so nice for the cylinder walls. An electric fuel pump at least re-fills the carb so it does start promptly.

Agree, most carbs running are not tuned just so... EFI should make a nice MPG gain in that situation.

 

We did a FiTech swap on our 400. It starts better, and has better response but didnt see much on the mileage. Getting 9-10 now was similar before although we "get on it" more now that it responds so well.